1. Field of the Invention
The present invention relates to methods and systems for concentrating metals into clusters within semiconductors, including novel structures and compositions of materials formed thereby, and also to the use of such clusters as sites for the collection and concentration of substances within such semiconductors. More particularly, the present invention relates to the concentration of transition metals in silicon into discrete clusters, the use of such clusters in internal gettering, and the resulting improvement in the properties of silicon.
2. Description of Prior Art
Silicon is one of the most abundant elements found within the earth's crust and is used in a variety of technical fields including integrated circuits (ICs), solar cells, micro electro mechanical systems (MEMS), and the like. The solar cell industry is growing rapidly and is responsible for an increasing amount of the silicon consumed, to the point that the silicon needs of the solar cell industry are starting to compete with the silicon needs of the IC industry. With present manufacturing technologies, both the IC and solar cell industries require a refined, purified, silicon feedstock as a starting material.
The purity requirements for the silicon feedstock for the solar cell industry are typically not as stringent at those for the IC industry. In fact, the solar cell industry can sometimes use recycled, scrapped, or rejected silicon material from the IC industry. However, metal impurities such as Fe, Ti, and the like are known to decrease the solar cell conversion efficiency leading to poor performance and a poor cost-to-performance ratio. These impurities may be removed utilizing a variety of well known techniques for purifying silicon, but this adds additional cost to the solar cell manufacturing process and reduces the profitability of the enterprise. Furthermore, if these impurities are homogeneously distributed throughout the material, the performance of the material in the solar cell application may be reduced. If the impurities can be concentrated and segregated into isolated regions within the material, the performance of the material as a solar cell may be improved even though the total amount of dangerous impurities within the material has not been reduced.
Therefore, there exists a need in the art to concentrate and/or isolate metal contaminants in a material, such as that used for the manufacture of solar cells, or to process the material in such a manner that the metal contaminants are less likely to have a negative effect on the performance of the material. Additionally, there exists a need to understand the structure, material composition and/or performance of the materials so that additional beneficial materials and systems can be conceived, developed, and employed for useful ends.